Book excerpt: The Learner's Perspective Study aims to juxtapose the observable practices of the classroom and the meanings attributed to those practices by classroom participants. The LPS research design documents sequences of at least ten lessons, using three video cameras, supplemented by the reconstructive accounts of classroom participants obtained in post-lesson video-stimulated interviews, and by test and questionnaire data, and copies of student written material. In each participating country, data generation focuses on the classrooms of three teachers, identified by the local mathematics education community as competent, and situated in demographically different school communities within the one major city. The large body of complex data supports both the characterisation of practice in the classrooms of competent teachers and the development of theory.